1. Technical Field
Example embodiments relate generally to semiconductor integrated circuit, and more particularly to a memory device for refresh and a memory system including the memory device.
2. Discussion of the Related Art
Semiconductor memory devices for storing data may be classified into volatile memory devices and non-volatile memory devices. Volatile memory devices, such as dynamic random access memory (DRAM) devices, are typically configured to store data by charging or discharging capacitors in memory cells, and lose the stored data when power is off. Non-volatile memory devices, such as flash memory devices, may maintain stored data even though power is off. Volatile memory devices are widely used as main memories of various apparatuses, while non-volatile memory devices are widely used for storing program code and/or data in various electronic devices, such as computers, mobile devices, etc.
In the volatile memory devices, cell charges stored in a memory cell may be lost by a leakage current. In addition, when a wordline is transitioned frequently between an active state and a precharged state, that is, when the wordline is accessed intensively or frequently, the affected memory cell connected to the adjacent wordline may lose the stored charges. The charges of the memory cell have to be recharged before the data are lost by the leakage of the cell charges. Such recharge of the cell charges is referred to as a refresh operation and the refresh operation often has to be performed repeatedly before the cell charges are lost significantly. In high-speed memory device, the time for refresh may become a major factor in decreasing the speed of the memory device.